Figure 1. Morphology of Phytophthora erythroseptica. Upper row, Nonpapillate sporangia; sympodium. Lower row, Homothallic oospores with amphigynous antheridia; internal and external proliferation. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996) Click image to see larger view.

 

Figure 2. Disease cycle of pink rot in potatoes caused by Phytophthora erythroseptica. (Courtesy Marlene Cameron and Phillip Wharton; Reproduced, by permission, from Wharton and Kirk, 2007) Click image to see larger view.

 

Figure 3. Culture of Phytophthora erythroseptica grown on V-8 juice agar. (Courtesy Jean B. Ristaino)

 

Figure 4. a, Oogonium of Phytophthora erythroseptica with an oospore and amphigynous antheridium. b, Sporangia of Phytophthora erythroseptica. (Courtesy Phillip Wharton; Reproduced, by permission, from Wharton and Kirk, 2007)

 

Figure 5. Oogonium and an amphigynous antheridium of Phytophthora erythroseptica (×1,000). (Courtesy Jean B. Ristaino)

 

Figure 6. Pink rot of potato caused by Phytophthora erythroseptica with external symptoms on the variety Reba. (Courtesy Thomas A. Zitter, Cornell University, Ithaca, NY)

 

Figure 7. The name pink rot describes the pink color that develops in infected tuber tissue when tubers are cut and exposed to the air for 15–30 min. (Courtesy Phillip Wharton; Reproduced, by permission, from Wharton and Kirk, 2007)

 

Figure 8. Pink rot of potato caused by Phytophthora erythroseptica with internal symptoms on the variety Reba. (Courtesy Thomas A. Zitter, Cornell University, Ithaca, NY)

 

Figure 9. When infected tubers are cut open the rotted portion is delimited by a dark line, visible through the tuber skin. (Courtesy Phillip Wharton; Reproduced, by permission, from Wharton and Kirk, 2007)

 

Figure 10. Infected tissues are easily invaded by secondary pathogens that produce the slimy symptoms often found in potatoes with pink rot. (Courtesy Phillip Wharton; Reproduced, by permission, from Wharton and Kirk, 2007)

 

Introduction

Phytophthora erythroseptica var. erythroseptica  Pethybr. (1913)

 

Phytophthora erythroseptica var. erythroseptica was first described by Pethybridge (1913; 1914) as the causal organism of pink rot of potatoes in Ireland. It is present in all potato-growing areas of the world. P. himalayensis Dastur (1948) and P. erythroseptica var. atropae Alcock (1926) are considered synonyms based on Waterhouse (1963). Kroon et al. (2004) and Cooke et al. (2000) demonstrated that P. erythroseptica is closely related to P. cryptogea based on molecular analysis. The variety P. erythroseptica var. pisi Bywater & Hickman (1959) on Pisum spp. has not been validly published and requires validation (Cline et al., 2008). The species was redescribed by Ho and Jong (1989). P. erythroseptica is a group VI species (Stamps, 1978; Stamps et al., 1990) (Figs. 1 and 2).

Cultural Characteristics

The minimum temperature for growth is 2.5°C, the optimum temperature for growth is 27.5°C, and the maximum temperature for growth is 34°C (Fig. 3).

Reproductive Structures

Asexual Structures

 

Sporangiophores:

Sporangiophores are sympodial and branch immediately below the sporangium. Sporangia proliferate internally through empty sporangia. Sympodia form in water.

 

Sporangia:

Sporangia are nonpapillate, vary from ellipsoid or ovoid to a distorted shape, and are often constricted in the middle. They are noncaducous. Sporangia are 26–47 × 43–69 µm (average 27.2 × 44.2 µm) with a round or tapered base (Fig. 4b). The length–breadth ratio is greater than 1.6.

 

Chlamydospores:

Chlamydospores have not been found.

 

Hyphae:

Hyphae are uniform, fine, and less than 8 µm. Rounded or angular swelling occurs in water.

 

Sexual Structures

 

P. erythroseptica is homothallic.

 

Antheridia:

Antheridia are amphigynous, elongated, ellipsoidal, or cylindrical and 13 × 14 µm in diameter. Oogonia with multiple antheridia (two to four) have been observed.

 

Oogonia:

Oogonia are smooth walled and 30–46 µm in diameter (average 34.9 µm).

 

Oospores:

Oospores are aplerotic and 28–35 µm in diameter (average 30.5 µm) with a thick wall (2.5 µm) (Figs. 4a and 5). 

Host Range and Distribution

Host

Common Name

Disease

Geographical Distribution

Atropa belladonna

Belladonna

Root rot; damping-off; seedling rot

Netherlands; United Kingdom

Brassica oleracea

Kale, cabbage, turnip

Root rot

Ireland

Carduus arvensis

Creeping thistle

Root rot

Ireland

Calceolaria spp.

Slipperwort, slipper flower

Root rot

New Zealand

Cymbidium spp.

Orchid

Root rot; leaf spot

Mexico, Australia, New Zealand

Cynosurus cristatus

Crested dogtail

Root rot

Ireland

Hordeum vulgare

Barley

Root rot

Ireland

Leymus chinensis

Chinese lyme grass

Crown and root rot

United States

Lolium multiflorum

Ryegrass

Root rot

Ireland

Lycopersicon esculentum

Tomato

Fruit rot

Canada

Phleum pratense

Timothy

Root rot

Ireland

Plantago media

Plantain

Root rot

Ireland

Saccharum officinarum

Sugarcane

Seed piece rot

United States

Secale cereale

Rye

Root rot

Ireland

Senecio cruentus

Cineraria

Wilt

New Zealand

Solanum tuberosum

Potato

Pink tuber rot

Ireland, Netherlands, United Kingdom, Indonesia, Bulgaria, Canada, Australia, United States, India, New Zealand, Yugoslavia, Tasmania, Egypt, Peru, Iran

Spinacia oleracea

Spinach

Seedling rot

Canada

Trifolium spp.

Clover

Root rot

United States

Tulipa spp.

Tulip

Root rot; shanking

United Kingdom, Greece

Tussilago farfara

Coltsfoot

Root rot

Ireland

Vicia faba, V. sativa

Broad bean, spring vetch

Root and crown rot

United States, Ireland

Zantedeschia spp.

White, yellow, or pink calla; arum lily

Rhizome rot; leaf and petiole blight

United States

Symptoms

The pathogen has been misidentified as the causal organism of red raspberry root rot. P. fragariae var. rubi is now recognized as the cause of raspberry root rot.

 

Pink Rot or Tuber Rot of Potato:

Pink rot occurs in potato tubers primarily, but the disease can affect stems, stolons, roots, and leaves of potato. Affected tubers have a dull brown appearance, and the lenticels and eyes turn dark brown (Fig. 6). Decay usually begins at the stem end of the tuber. When the tuber is cut, the exposed surface turns deep salmon pink after 30–45 min (Figs. 7 and 8). Potato tubers become tough and leathery after infection (Fig. 9). Dormant oospores initiate disease from infested soil (Erwin and Ribeiro, 1996) (Fig. 10).

 

Seed-Piece Rot of Sugarcane:

Infection of sugarcane stem pieces in Louisiana have been reported to be caused by P. erythroseptica. Infected tissues become water-soaked. Salmon pink to orange-red streaks appear throughout the interior of the stalk as the disease progresses. In advanced stages, the whole cane becomes water-soaked and turns reddish brown, giving off an etherlike smell. The disease has only been reported in the United States. P. megasperma has also been isolated from decaying stem pieces and is more virulent that P. erythroseptica on sugarcane (van der Zwet and Forbes, 1961).

References

Alcock, N. 1926. A preliminary note on a Phytophthora on Atropa belladonna. Pharm. J. 116:232.

 

Bywater, J., and Hickman, C. J. 1959. A new variety of Phytophthora erythroseptica, which causes a soft rot of pea roots. Trans. Br. Mycol. Soc. 42:513-524.

 

Cline, E. T., Farr, D. F., and Rossman, A. Y. 2008. A synopsis of Phytophthora with accurate scientific names, host range, and geographic distribution. Plant Health Progress. doi:10.1094/PHP-2008-0318-01-RS.

 

Cooke, D. E. L., Drenth, A., Duncan, J. M., Wagels, G., and Brasier, C. M. 2000. A molecular phylogeny of Phytophthora and related oomycetes. Fungal Genet. Biol. 30:17-32.

 

Dastur, J. F. 1948. Phytophthora species of potatoes (Solanum tuberosum) in the Simla Hills. Indian Phytopathol. 1:19-26.

 

Erwin, D. C., and Ribeiro, O. K. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.

 

Ho, H. H., and Jong, S. C. 1989. Phytophthora erythroseptica. Mycotaxon 36:73-90.

 

Kroon, L. P. N. M., Bakker, F. T., van den Bosch, G. B. M., Bonants, P. J. M., and Flier, W. G. 2004. Phylogenetic analysis of Phytophthora species based on mitochondrial and nuclear DNA sequences. Fungal Genet. Biol. 41:766-782.

 

Pethybridge, G. H. 1913. On the rotting of potato tubers by a new species of Phytophthora having a method of sexual reproduction hitherto undescribed. Sci. Proc. R. Dublin Soc. 13:529-565.

 

Pethybridge, G. H. 1914. Further observations on Phytophthora erythroseptica Pethybr. and on the disease produced by it in the potato plant. Sci. Proc. R. Dublin Soc. 14:179-198.

 

Stamps, D. J. 1978. Phytophthora erythroseptica. CMI Descr. Pathog. Fungi Bact. 593:1-2.

 

Stamps, D. J., Newhook, F. J., Waterhouse, G. M., and Hall, G. S. 1990. Revised tabular key to the species of Phytophthora de Bary. Mycol. Pap. 162. CAB International, Wallingford, United Kingdom; Commonwealth Mycological Institute, Kew, Surrey, England.

 

van der Zwet, T., and Forbes, I. L. 1961. Phytophthora megasperma. The principal cause of seed-piece rot of sugarcane in Louisiana. Phytopathology 51:634-640.

 

Waterhouse, G. M. 1963. Key to the species of Phytophthora de Bary. Mycol. Pap. 92. CAB International, Wallingford, United Kingdom; Commonwealth Mycological Institute, Kew, Surrey, England.

 

Wharton, P., and Kirk, W. 2007. Pink Rot. Michigan Potato Diseases Series. Mich. State Univ. Ext. Bull. E-2993. www.potatodiseases.org/pinkrot.html.